15 with no max is max for DWA. Cant use Gyro due to Build Effect. Mods cant stack with units or mods that have effects. So if you gave DWA the ability "No Max Ballistic Range" then it could take weapons up to 15.

Secondary weapons could be
Gyrojet Long-gun with a max range of 14 -- Using SGA/Balanced
Neptune with a max range of 15 -- Using SGA/Gyro/Balanced/Nept mod layout